As a protocol to make a packet relay device such as a router device and a layer 3 (L3) switch redundant, a virtual router redundancy protocol (VRRP) is known. In the VRRP, priority levels are respectively set to a plurality of packet relay devices that belong to the same group. A packet relay device to which the highest priority level is set is called, for example, a master or an active system. Such a packet relay device becomes in an operation state and relays a data packet.
In addition, a packet relay device other than the master is called, for example, a slave, a standby system or a backup. The slave packet relay device is in a standby state. The state of the slave packet relay device becomes from the standby state to an operation state, and the slave packet relay device functions as a master when failure occurs in the master packet relay device. When there are a plurality of slave packet relay devices, order of transition to a master is determined depending on the set priority level. As described above, relay of a data packet, which has been performed in the master packet relay device, is performed in the packet relay device that has transitioned from the slave to the master. As the related art, for example, Japanese Laid-open Patent Publication No. 2006-310903 has been discussed.